An example of such an agitation apparatus has a cylindrically shaped agitation vessel, and a substantially cylindrically shaped agitation member that has an outer diameter smaller than the inner diameter of the agitation vessel and rotates concentrically with the inner circumferential surface of the agitation vessel. The agitation member has a multiplicity of small holes formed in radial directions through its cylindrical portion. In the agitation apparatus, the agitation member rotates at high speed while keeping a very small clearance from the inner circumferential surface of the agitation vessel. In association with the high-speed rotation of the agitation member, a centrifugal force acts on a material supplied to the agitation vessel. By the centrifugal force, the material is forced out in radially outward directions through the small holes formed in the agitation member, and is spread in a tubular thin film shape into a gap between the outer circumferential surface of the agitation member and the inner circumferential surface of the agitation vessel. At that time, the material is agitated between the surface of the material and the inner circumferential surface of the agitation vessel. Then, the material that has been agitated sufficiently to lower its viscosity is moved to the upper portion of the agitation vessel by the centrifugal force and is discharged from the upper portion of the agitation vessel.
This type of agitation apparatus is disclosed in, for example, JP 3256801 B (Patent Literature 1), JP 2005-129482 A (Patent Literature 2), JP 2006-236658 A (Patent Literature 3), and JP 2007-125454 A (Patent Literature 4).